This is a 35 USC application of PCT/DE 00/00105 filed on Jan. 13, 2000.
The invention is based on a fuel injection system for an internal combustion engine, the fuel injection system having two high pressure pumps that supply fuel to the injection system at different pressures.
One such fuel injection system is disclosed for instance in WO 98/09068 A1.
The use of fuel injection systems with pressure reservoirs is known in diesel engines and in direct gasoline injection engines. These systems employ a high-pressure pump and sometimes a prefeed pump which preferred pump supplies fuel at pressure of up to about 10 bar). Systems with intake throttle regulation are also known.
In the injectors for the injection of the diesel fuel, a distinction is presently made between stroke- and pressure-controlled systems. In a pressure-controlled fuel injection system, a valve body (such as a nozzle) is open by the fuel pressure in the nozzle chamber of the injector controlled fuel injection system, the opening and closing of the injection opening is effected with the aid of a valve body on the basis of the hydraulic cooperation of two fuel pressures, one in the nozzle chamber and the other in a control chamber. The pressure at which fuel emerges from the nozzle chamber into the cylinder is called the injection pressure, while the pressure at which the fuel is available or is stored in the injection system is called the system pressure. As for the injectors, there are also injection nozzles with a variable injection port cross section (vario-nozzle) and with a two-stage nozzle needle stroke.
In the stroke-controlled injection system known from WO 98/09068 A1, fuel from a fuel tank is compressed to two different, high system pressures, each by means of a different pump, and fed into a respective pressure reservoirs. Via a valve control, either the higher or the lower system pressure can be carried into the nozzle chamber of an injector.
From European Patent Disclosure EP 0 711 914 A1, a pressure-controlled injection system is also known, in which with the aid of a high-pressure pump, fuel is compressed to a first, high system pressure of about 1200 bar and stored in a first pressure reservoir. The fuel at high pressure is also fed into a second pressure reservoir, in which by regulation of its fuel delivery by means of a 2/2-way valve, a second high system pressure of approximately 400 bar is maintained. Via a valve control unit, either the lower or the higher system pressure can be carried into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can emerge from the nozzle opening.
Because of the capability of having two pressures, or two pumping stages available, the lower system pressure (first high-pressure stage) can be used to seal against the leakage quantity from the second pressure stage (higher system pressure). Both pumps are preferably accommodated in one housing.
The pressure of the first high-pressure stage (for instance, approximately 200 bar) can, for instance, be utilized to enable a hydraulic valve adjustment of the inlet and outlet valves, enable adjustment of the camshaft, enable actuation of engine braking systems, and so forth. Also with the pressure of the first high-pressure stage, a preinjection and/or a postinjection of fuel can be achieved to help control emissions.
For certain applications, such as in Otto engines, a hydraulic step-up from fuel pressure to lubricating oil pressure or vice versa can be done selectively in the first and second high-pressure stage, respectively. There is also the capability of using the pressure of the first high-pressure stage to control the opening cross section or to trigger injection nozzles (control pressure) under stroke or pressure control. The control of the stroke can be done quite simply via pressure/travel (spring force) or via a fixed stop. The pressures can be switched via piezoelectric or magnet valves, and the control pressure for all the cylinders can be switched either centrally via one valve or locally via a plurality of valves. With the control pressure of the first high-pressure stage, a vario-nozzle can for instance also be triggered. The system is suitable for both Otto and diesel engines.
The fuel injection system of the present invention furthermore enables the following:
better efficiency in comparison to systems with only one high-pressure pump or high-pressure stage.
better sealing off of the pump from higher pressures.
control of systems present in the engine, such as inlet and outlet devices, via the fuel system.
a compact structure. Piezoelectric or magnet valves can be provided on the pressure reservoir or pressure reservoirs and need not be disposed directly in or on the nozzle holder in the cylinder head.
triggering of injection nozzles under pressure or stroke control and also infinitely variably or via a stroke stop, regardless of the injection pressure.
low electrical power for actuating piezoelectric or magnet valves, since low control pressures and short travel distances are possible.
a modular design.
the fact that the system is free in terms of the choice of the injection onset. Both preinjection and postinjection of fuel are therefore possible.
the use of the pressure of the first high-pressure stage for a preinjection and/or postinjection. Because of the low injection pressure, soot development and oil thinning are largely avoided.
Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims.